1. Field of the Invention
This invention relates to compositions which cure at room temperature to elastomeric type products useful as sealants.
2. Background Information
Many kinds of very useful compositions cure at room temperature to elastomeric materials having a broad spectrum of physical and chemical properties. However, with every desirable property, there seems to be undesirable properties and one is continually faced with the problem of choosing the right composition for the specific application. The application to which room temperature curing compositions can be put, keep increasing, and with the increasing variety of applications, the specific kinds of properties required, keep changing. The need for new room temperature curing compositions with new properties is thus in demand. The market is continually looking for the new desirable properties without the same previous undesirable properties.
One kind of room temperature curing composition is described by Sweet in U.S. Pat. No. 3,189,576, issued June 15, 1965. Sweet describes oxime silane crosslinkers which are useful to make room temperature curing compositions. Oximo and ketoximo are considered the same group. Sweet teaches trifunctional ketoximo silanes and tetrafunotional ketoximo silanes as crosslinkers. These crosslinkers can be used to make room temperature curing silicone elastomeric compositions by mixing them with hydroxyl endblocked polydiorganosiloxane. The compositions can also contain fillers and curing catalysts. The Sweet method of making the ketoximo silanes is reacting chlorosilanes with ketoxime in the presence of an acid acceptor. This method can be used to make the silanes, but the method was found to be hazardous because it produced an exotherm which could result in an explosion. Although the resulting products are desirable, the method limited the usefulness of the ketoximo silanes as crosslinkers in room temperature curing compositions. Von Au et al in U.S. Pat. No. 4,503,210, issued Mar. 5, 1985, teach oxime containing compositions containing silicon compounds with three and four oxime groups per molecule.
Wada et al. in Japanese Patent Publication No. 49[1974]39967, published Oct. 30, 1974, teach oxime containing silanes. Wada et al. teach that the method of manufacturing organosilanes containing oxime groups bonded directly to the silicon atom is reacting tetrachlorosilanes and methyltrichlorosilanes with oximes in the presence of an acid acceptor and a solvent. Wada et al. teach that this method had some difficulties. Wada et al. report that the method requires a tremendous quantity of solvent, a tremendous quantity of amine which is toxic and has a disagreeable odor, requires an anhydrous environment, requires special equipment to filter the reaction product and keep the conditions anhydrous, and requires extremely difficult measures to remove the salts of amine and hydrogen chloride. Wada et al. teach that these shortcomings can be overcome if the following method for the manufacture of organosilanes which contain oxime bonded directly to silicon atoms is used. This new method by Wada et al. is demethanolating R'.sub.a Si(OCH3).sub.4-a with an oxime of the formula X.dbd.NOH, where a is 0 or 1, R' is hydrocarbon, halogenated hydrocarbon, or cyanohydrocarbon, and X is R'.sub.2 C.dbd. or R"C.dbd. where R" is a divalent hydrocarbon group or halogenated hydrocarbon group. A catalyst can be used if necessary for the demethanolation. The product obtained by Wada et al. has the following formula EQU R'.sub.a Si(OCH.sub.3).sub.b (ON.dbd.X).sub.4-(a+b).
Wada et al. teach that it is conceivable to use alkoxysilanes such as ethoxysilane, propoxysilane, and butoxysilane instead of the starting methoxysilane, but that none of these other alkoxysilanes seem appropriate for use in their method. For example, when ethoxysilane is used, the deethanolating reaction proceeds minimally and it is difficult to obtain the intended organosilane which contains an oxime group. Wada et al. report that the propoxysilane and the butoxysilane hardly react at all. In an example, Wada et al teach a composition made by kneading methylmethoxydioximosilane, dimethylpolysiloxane having hydroxy groups on both molecular chain terminals, fumed silica, and dibutyl tin dilaurate. This composition is reported to cure to a hardened rubber elastomer after 24 hours.
Hashimoto in U.S. Pat. No. 4,371,682, issued Feb. 1, 1983, teaches a room temperature curable polyorganosiloxane composition containing as the crosslinker an oxime containing compound produced by an oxime radical-methoxyl radical exchange reaction using an oxime radical containing compound of the formula EQU R'.sub.a Si(ON.dbd.X).sub.4-a
in which a is 0 or 1 and a methoxyl radical containing compound of the formula EQU R'.sub.b Si(OCH3).sub.4-b
in which b is 0 or 1 and the ratio of the oxime radical to the methoxyl radical is from 1:0.2 to 1:2. Hashimoto teaches that using the reaction product provides a room temperature curing composition which cures faster when exposed to moisture. Hashimoto's composition requires the presence of a curing catalyst in order to obtain a cured product in a short period of time.
Chempolil et al. in European Patent Application No. 98,369, published January 18, 1984, teach a process for making alkoxyoximosilanes by reacting a silicon halide of the formula R.sub.4-n SiY.sub.n where n is an integer of 2 to 4 with an alcohol having 1 to 24 carbon atoms and an oxime of the formula R'2C.dbd.NOH to produce at least one alkoxyoximosilane of the formula EQU R.sub.4-n Si(OR).sub.p (ON.dbd.CR'.sub.2).sub.n-p
where p is an integer of 1 to 3, but is at least one less than n and the hydrohalide of the oxime by-product. The molar ratio of alcohol to silicon halide is m:1, wherein m is at least 0.1 n and less than n. and the molar ratio of oxime to silicon halide is at least (2n-m):1. Chempolil et al.. however, do not show any tetrafunctional silanes and the resulting products. The difficulty with chlorosilanes and by-products has not been overcome by the process of Chempolil et al.
Klosowski et al in U.S. Pat. No. 4,657,967, issued Apr. 14, 1987, teach room temperature curing compositions containing tetrafunctional ethoxy-ketoximo silane crosslinkers. The crosslinkers of Klosowski et al are described as a mixture of species which is 0 to 80 weight percent tetraketoximosilane, 20 to 70 weight percent monoethoxytriketoximosilane, 1 to 60 weight percent diethoxydiketoximosilane, and 0 to 20 weight percent triethoxymonoketoximosilane as the broad range. Klosowski et al teach that the preferred range of species in the mixture are 2 to 40 weight percent tetraketoximosilane, 45 to 65 monoethoxytriketoximosilane, 8 to 45 diethoxydiketoximosilane, and 0 to 8 weight percent triethoxymonoketoximosilane. Klosowski et al also teach that the compositions are made up of hydroxyl endblocked polydiorganosiloxane and the tetrafunctional ethoxy-ketoximo silane crosslinker, optionally a filler can be present. They teach that such compositions cure rapidly at room temperature when exposed to moisture, but that if even faster curing is required that a curing catalyst can be used. Klosowski et al caution that curing catalyst which cause reversion should not be used, such catalyst include amines and metal carboxylates, such as dibutyltindiacetate, dibutyltindilaurate, and stannous octoate, lead carboxylates and zinc carboxylates. Klosowski et al teach that non-reversion catalyst should be used such as organotitanates. They teach that an advantage of their compositions is that they cure rapidly without the presence of a curing catalyst, especially without a tin catalyst or other catalyst which can cause reversion.